System and method for reducing auditory perception of noise associated with a medical imaging process

ABSTRACT

A system and method for acoustic noise reduction/cancellation is disclosed that includes a medical imaging scanner configured to scan an imaging subject within an imaging area that emits system noise when in operation. An ultrasonic emitter system is included that is constructed to emit an inaudible signal having properties to reduce perception of the system noise about at least a portion of the imaging area.

BACKGROUND OF INVENTION

The present invention relates generally to medical imaging devices, andmore particularly, to a system and method using a parametric signalgenerator to reduce perceivable noise generated during operation of amedical imaging device.

When a substance such as human tissue is subjected to a uniform magneticfield (polarizing field B₀), the individual magnetic moments of thespins in the tissue attempt to align with this polarizing field, butprocess about it in random order at their characteristic Larmorfrequency. If the substance, or tissue, is subjected to a magnetic field(excitation field B₁) which is in the x-y plane and which is near theLarmor frequency, the net aligned moment, or “longitudinalmagnetization,” M_(Z), may be rotated, or “tipped,” into the x-y planeto produce a net transverse magnetic moment M_(t). A signal is emittedby the excited spins after the excitation signal B₁ is terminated. Thissignal may be received and processed to form an image by application ofa combination of linear gradient fields (Bx, By and Bz) as produced bythe gradient coils. These fields cause the individual spins in the humantissue to precess at different frequencies (Larmor relationship) andthese differences can be used to encode the raw data to provide realimages.

As current is introduced to the gradient coils, such as to produce theBx, By or Bz fields, an acoustic noise is created by Lorentz forces.This noise can be rather loud and might be described to those notskilled in the art as akin to beating of an empty drum with a hammer.While the production of noise in this manner does not directly affectthe medical imaging process, the noise may be uncomfortable ordisconcerting to an imaging subject. Accordingly, “noise cancellation”devices have been developed in an attempt to reduce the imagingsubject's perception of the noise and thereby present a more comfortableenvironment for the subject during the imaging process. However, priornoise cancellation devices and methods have not met general acceptancefor a number of reasons.

For example, attempts to utilize conventional sound production devicessuch as loud speakers to produce acoustic noise canceling signalsdesigned to reduce an imaging subject's perception of noise have beenlargely unsuccessful for various reasons. First, conventional loudspeakers become ineffective when subjected to strong magnetic fieldssuch as those produced by the imaging process. That is, the magneticfield generated during the imaging process interacts with the voicecoils in the loud speaker and interferes with proper emission of thedesired noise canceling signal from the loud speaker. Second,conventional loud speakers emit audible signals that can be difficult tocontrol as the audio signal disperses peripherally during propagation.As such, by removing the loud speakers from close proximity to theimaging device in an attempt to lessen the effects of the magnetic fieldproduced by the imaging device, the audio may “bleedthrough” toundesired areas and may actually create more unwanted noise. Therefore,while extending the distance between the loudspeaker system and theimaging device lowers the effects of the field, the extended distancecauses the noise reducing signal to further dissipate and disperse intounwanted areas.

Additionally, attempts have been made to construct noise reducingsystems utilizing pneumatically driven or air driven signals, such asthose found in commercial airline applications. These systems areadvantageous because they can provide a highly directional signal to anarea without the use of conductive materials that can be adverselyaffected by the magnetic field generated during imaging. However,pneumatically driven systems typically do not deliver signals accuratelyenough to sufficiently reduce noise generated by the imaging process.Therefore, while a headset may be made of plastic, glass, or some othernon-conductive material such that signal delivery is highly directed andis unimpaired by magnetic fields, the accuracy of the signal deliveredis insufficient to serve as a suitable noise canceling means.

Alternate audio producing systems such as piezoelectric speakers havealso been found to be unsuitable for such noise canceling applicationdue to inherent limitations at low frequency ranges. As such, thoughpiezoelectric speakers are not impeded by the magnetic fields associatedwith medical imaging, suitable noise cancellation fails at the necessarylow frequencies generated by the Lorentz forces on the gradient coils.Therefore, the low frequencies produced as a byproduct of the imagingprocess are unaffected and remain perceivable by the imaging subject.

It would therefore be desirable to have a system and method capable ofgenerating suitable noise cancellation signals to reduce the perceivednoise associated with medical imaging processes such as MR imaging.Furthermore, it would be advantageous to have a system and methodcapable of directionally controlling the emission of a noisecancellation signal to avoid unnecessary propagation of noisecancellation signals into undesired areas. Also, it would be desiredthat such a system and method be capable of generating the necessarynoise reducing signal without substantial operational impairment by themagnetic field.

BRIEF DESCRIPTION OF INVENTION

The present invention provides a system and method of reducing theperception of noise generated as a byproduct of a medical imagingprocess through acoustic noise cancellation. The inaudible signal isgenerated by a parametric signal generator and is emitted and directedto a selected area wherein the perceivable noise within the area issignificantly reduced.

In accordance with one aspect of the invention, a medical imagingscanner system is disclosed that is configured to scan an imagingsubject within an imaging area that emits system noise when inoperation. The medical imaging scanner system includes an emitter systemconstructed to emit an inaudible signal having properties to reduceperception of the system noise about at least a portion of the imagingarea.

In accordance with another aspect of the invention, a method of medicalimaging is disclosed that includes performing a medical imaging processupon an imaging subject. This medical imaging process typically producesan undesirable noise byproduct. The method of medical imaging includesemitting an audible signal configured to diminish auditory perception ofthe noise byproduct.

In accordance with yet another aspect of the invention, an MRI apparatusincluding an MRI system is disclosed that includes a plurality ofgradient coils positioned about a bore of polarizing magnet to impress apolarizing magnetic field. The MRI system also includes an RFtransceiver system and an RF switch controlled by a pulse module totransmit RF signal to an RF coil assembly to acquire MR images. The MRIapparatus further includes a parametric signal generator configured togenerate ultrasonic signals to reduce perception of noise produced bythe MRI system during operation.

Various other features, objects, and advantages of the present inventionwill be made apparent from the following detailed description and thedrawings.

BRIEF DESCRIPTION OF DRAWINGS

The drawings illustrate one preferred embodiment presently contemplatedfor carrying out the invention.

In the drawings:

FIG. 1 is a schematic block diagram of an MR imaging system for use withthe present invention.

FIG. 2 is a block diagram of a directional noise perception reductionsystem for use with the MR imaging system of FIG. 1.

FIG. 3 is a flow chart showing the steps of a noise perception reductiontechnique in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

A system and method is disclosed to reduce perception of noise producedas a byproduct of an imaging process using a directional inaudiblesignal. An emitter is used to emit an inaudible signal that hasproperties designed to reduce noise produced by an imaging system aboutat least a portion of an imaging subject.

Referring to FIG. 1, the major components of a preferred magneticresonance imaging (MRI) system 10 incorporating the present inventionare shown. The operation of the system is controlled from an operatorconsole 12 which includes a keyboard or other input device 13, a controlpanel 14, and a display screen 16. The console 12 communicates through alink 18 with a separate computer system 20 that enables an operator tocontrol the production and display of images on the display screen 16.The computer system 20 includes a number of modules which communicatewith each other through a backplane 20 a. These include an imageprocessor module 22, a CPU module 24 and a memory module 26, known inthe art as a frame buffer for storing image data arrays. The computersystem 20 is linked to disk storage 28 and tape drive 30 for storage ofimage data and programs, and communicates with a separate system control32 through a high speed serial link 34. The input device 13 can includea mouse, joystick, keyboard, track ball, touch activated screen, lightwand, voice control, or any similar or equivalent input device, and maybe used for interactive geometry prescription.

The system control 32 includes a set of modules connected together by abackplane 32 a. These include a CPU module 36 and a pulse generatormodule 38 which connects to the operator console 12 through a seriallink 40. It is through link 40 that the system control 32 receivescommands from the operator to indicate the scan sequence that is to beperformed. The pulse generator module 38 operates the system componentsto carry out the desired scan sequence and produces data which indicatesthe timing, strength and shape of the RF pulses produced, and the timingand length of the data acquisition window. The pulse generator module 38connects to a set of gradient amplifiers 42, to indicate the timing andshape of the gradient pulses that are produced during the scan. Thepulse generator module 38 can also receive patient data from aphysiological acquisition controller 44 that receives signals from anumber of different sensors connected to the patient, such as ECGsignals from electrodes attached to the patient. And finally, the pulsegenerator module 38 connects to a scan room interface circuit 46 whichreceives signals from various sensors associated with the condition ofthe patient and the magnet system. It is also through the scan roominterface circuit 46 that a patient positioning system 48 receivescommands to move the patient to the desired position for the scan.

The gradient waveforms produced by the pulse generator module 38 areapplied to the gradient amplifier system 42 having G_(x), G_(y), andG_(z) amplifiers. Each gradient amplifier excites a correspondingphysical gradient coil in a gradient coil assembly generally designated50 to produce the magnetic field gradients used for spatially encodingacquired signals. The gradient coil assembly 50 forms part of a magnetassembly 52 which includes a polarizing magnet 54 and a whole-body RFcoil 56. A transceiver module 58 in the system control 32 producespulses which are amplified by an RF amplifier 60 and coupled to the RFcoil 56 by a transmit/receive switch 62. The resulting signals emittedby the excited nuclei in the patient may be sensed by the same RF coil56 and coupled through the transmit/receive switch 62 to a preamplifier64. The amplified MR signals are demodulated, filtered, and digitized inthe receiver section of the transceiver 58. The transmit/receive switch62 is controlled by a signal from the pulse generator module 38 toelectrically connect the RF amplifier 60 to the coil 56 during thetransmit mode and to connect the preamplifier 64 to the coil 56 duringthe receive mode. The transmit/receive switch 62 can also enable aseparate RF coil (for example, a surface coil) to be used in either thetransmit or receive mode.

The MR signals picked up by the RF coil 56 are digitized by thetransceiver module 58 and transferred to a memory module 66 in thesystem control 32. A scan is complete when an array of raw k-space datahas been acquired in the memory module 66. This raw k-space data isrearranged into separate k-space data arrays for each image to bereconstructed, and each of these is input to an array processor 68 whichoperates to Fourier transform the data into an array of image data. Thisimage data is conveyed through the serial link 34 to the computer system20 where it is stored in memory, such as disk storage 28. In response tocommands received from the operator console 12, this image data may bearchived in long term storage, such as on the tape drive 30, or it maybe further processed by the image processor 22 and conveyed to theoperator console 12 and presented on the display 16.

The MRI system 10 also has a noise detection device 70, signal generator71, and emitter system 72. The noise detection device 70 is configuredto monitor the MRI system 10 during operation and detect certain noiseassociated with the operation. The noise detection device 70 sendsfeedback regarding detected noise to a signal generator 71. The signalgenerator 71 reviews the feedback from the noise detector device 70 anddetermines the properties of a signal necessary to reduce auditoryperception of the detected noise. The signal generator 71 generates asignal with properties to reduce perception of the system noise createdas a byproduct of an imaging process. The signal generator 71 sends thegenerated signal to an emitter system 72 for processing and emission.

The signal generator 71 and the emitter system 72 together function as aparamagnetic signal generator. That is, as will be described in greaterdetail with respect to FIG. 2, the emitter system 72 receives the signalproduced by the signal generator 71. Using this signal, the emittersystem 72 creates an ultrasonic signal with a frequency preferablygreater than approximately 2 kHz that when introduced to a non-linearmedium, such as air, is converted from a set of ultrasonic frequenciesto an audible signal designed to reduce auditory perception of theimaging system 10 noise.

The emitter system 72 is designed to emit the inaudible signal as acolumn to produce anti-noise or noise canceling signals that reduce theauditory noise perceived by an imaging subject 76. The inaudible signal74 is designed to be demodulated by a non-linear medium. Therefore, whenthe inaudible signal 24 is emitted from the emitter system 72, thesignal is demodulated by an interaction with environmental air, whichhas non-linear properties. The demodulation produces audible tones in ahighly directional column that may be directed at the imaging subject 76to at least partially cancel noise produced by the operation of MRIsystem 10.

It is contemplated that the emitter system 72 and/or components thereofmay be positioned within the magnetic field generated by the coils 50 ormay be positioned outside the field. In a preferred embodiment, theemitter system includes a HyperSonic®Sound (HSS®) emitter, as availablein American Technology Corporation's R220A system, to generate theinaudible signal. The emitter is based on piezoelectric technology whichis not subject to the low frequency limitations described earlier sinceit is used to create ultrasonic frequency signals. HyperSonic® Sound andHSS® are registered trademarks of American Technology Corporation, 12725Stowe Drive Poway, Califormia 92064. The HSS® emitter may be positionedremoved from, but in proximity to, the coils 50 to emit the inaudiblesignal at the imaging subject 76.

FIG. 2 illustrates an embodiment of the noise detection device 70,signal generator 71, and emitter system 72 that together deliver ahighly directional inaudible signal designed to reduce perceivable noisegenerated during an imaging process. The emitter system 72, inaccordance with a preferred embodiment, includes a signal processor 78,a distortion control 80, a modulator 82, an amplifier 84, and an emitter86.

In response to feedback from the noise detection device 70, indicatingthat noise is currently or is about to be generated as a byproduct of animaging process, the signal generator 71 generates a signal withproperties specifically designed to reduce the noise detected by thenoise detection device 70. The signal frequency generated is dependentupon the noise produced as a byproduct of an imaging process and thefeedback received regarding such noise.

It is contemplated that prior to any noise generation from the MRsystem, a look-up table may be utilized, whereby the characteristics ofa selected imaging sequence are used to look up information from thelook-up table regarding noise characteristics of the selected imagingsequence. The characteristics of the noise byproduct produced aredirectly related to the pulse sequence used in specific imaging processand will vary substantially according to the scan selected. Therefore,the selected imaging process may be utilized to predict the noisecharacteristics that will be associated therewith and predictivelydetermine the signal characteristics necessary to reduce the perceivablenoise produced as a byproduct of the selected imaging process.

Additionally or alternatively, once the imaging process has begun andnoise byproduct is being generated, the signal generator 71 analyzes thenoise detected. By analyzing the noise detected by the noise detectionsystem 70, the signal generator 71 dynamically determines thecharacteristics of a signal necessary to reduce perception of the noisebyproduct. It is contemplated that the signal generator 71 continue theanalysis over the duration of the imaging process to dynamically adjustto changes in the noise byproduct to reduce auditory perception of thenoise byproduct regardless of variations in the noise characteristics.

Once the signal generator 71 determines the necessary signal, the signalis passed to the emitter system 72. Upon reaching the emitter system 72,the signal is passed through a signal processor 78, distortion control80, and a modulator 82 to form a composite inaudible or ultrasonicwaveform. Specifically, the signal processor 78 receives the signalgenerated by the signal generator 71 and generates an ultrasonicfrequency signal, which is modulated by the modulator 82 with a secondsignal that may or may not be ultrasonic to create a compositeultrasonic waveform. The composite ultrasonic waveform is provided tothe amplifier 84 to generate an amplified composite ultrasonic waveformthat is passed to the emitter 86. The amplified composite ultrasonicwaveform is output from emitter 86 as a highly directional inaudiblesignal column 74. That is, the emitted inaudible signal 74 forms avirtual column directly in front of emitter 86.

Upon impinging a non-linear medium 88, such as atmospheric air, theinaudible signal 74 interacts with the air. The non-linearity of the air88 demodulates the inaudible signal 74 generating canceling audiblesounds 90. These audible sounds 90 are generated due to properties ofthe non-linear medium, i.e. air, though which the column of inaudiblesignal 74 passes. Specifically, the non-linear medium “down converts”the inaudible signal 74 to a lower audible frequency spectrum, therebyconverting the inaudible signal column 74 to an audible signal column90.

Therefore, in response to noise feedback, the signal generator 71generates a signal designed to reduce perceived noise produced as abyproduct of an imaging process. The signal passes through a signalprocessor 78, a distortion control 80, and a modulator 82 to produce acomposite ultrasonic waveform. The composite ultrasonic waveform passesto an amplifier 84 before being passed from an emitter 86. As theemitted inaudible signal 74 passes through a non-linear medium 88, suchas air, the signal 74 is demodulated by an interaction with thenon-linear medium 88 to produce audible tones 90 that are designed to atleast reduce an imaging subject's perception of noise produced as abyproduct of an imaging process. The ultrasonic signal 74 and ultimatelythe audible signal 90 travel as highly directional signals that may becontrolled as a column to be directed toward an imaging subject and/orany other target without significant signal dispersion and associatedbleed-through.

Referring now to FIG. 3, a flowchart 100 is shown illustrating the stepsof a technique for reducing the noise perceived by an imaging subjectduring an imaging process. The technique starts 100 upon initiation orselection of a desired imaging process 104. Once the desired imagingprocess is selected 104, the noise generated as a byproduct of theimaging process is predicted and/or detected, as described with respectto FIG. 2. That is, as previously described, a look-up table may beutilized to predict the noise that will be produced by the imagingprocess and then the noise generated as a byproduct of the initiatedimaging process may be continuously detected to dynamically generate anoise reducing signal during the imaging process 106.

The noise prediction/detection 106 is used to determine the specificsignal to generate so as to include properties selected to ultimatelyreduce the noise byproduct perceived by the imaging subject 108. Theselected signal 108 is then processed, as described with respect to FIG.2, and emitted as an inaudible signal column 112.

To assure that changes in the noise byproduct do not deviate from thepredicted/detected noise 106, a check is made to determine whether theimaging process is complete 114. If the process is not yet complete 116,the system again determines the noise byproduct produced by the imagingprocess 106 to continually determine and adjust the source signal inresponse to changes in the generated system noise. As such, the systemdynamically adjusts to changes in the characteristics of the noisebyproduct to assure that the noise perceived by the imaging subject issufficiently reduced. On the other hand, once the imaging process iscomplete 116, the technique ends 120 and signal emissions cease.

Therefore, the above-described system and method generates a highlydirectionally controlled signal that is designed to reduce noiseperceived by an imaging subject during an imaging process. The signalsproduced are dynamically generated and emitted as an ultrasonic signalthat, upon interaction with air, generates an audible signal thatreduces noise perceived by an imaging subject across a varying spectrumof noise. Additionally, the above-described system is designed such thatthe signals generated and the system for emitting the signals areunimpeded by strong magnetic fields that may be associated with theimaging process. It is contemplated that while the present invention isparticularly applicable in an MR imaging system, the system performingthe imaging process may also include an ultrasound imaging system, anx-ray imaging system, a computed tomography (CT) imaging system, anelectron beam tomography system, a positron emission tomography system,a single photon emission computed tomography system, or any otherimaging system that may benefit from noise reduction.

Therefore, the present invention provides a system and method ofreducing perceivable noise generated as a byproduct of a medical imagingprocess through acoustic noise cancellation. A parametric signalgenerator is used to generate an inaudible signal that has propertiesdesigned to reduce noise produced by an imaging system about at least aportion of an imaging subject.

In accordance with one embodiment of the invention, a medical imagingscanner system is configured to scan an imaging subject within animaging area. The medical imaging scanner emits system noise when inoperation. The medical imaging scanner system also includes an emittersystem constructed to emit an inaudible signal having properties toreduce perception of the system noise about at least a portion of theimaging area.

Another embodiment of the invention includes a method of medicalimaging. The method includes performing a medical imaging process uponan imaging subject, wherein the medical imaging process produces a noisebyproduct. The method of medical imaging includes emitting an audiblesignal configured to diminish auditory perception of the noisebyproduct.

In a further embodiment of the invention, an MRI apparatus includes anMRI system having a plurality of gradient coils positioned about a boreof polarizing magnet to impress a polarizing magnetic field. The MRIsystem also has an RF transceiver system and an RF switch controlled bya pulse module to transmit RF signal to an RF coil assembly to acquireMR images. Also, the MRI apparatus includes a parametric signalgenerator configured to generate ultrasonic signals to reduce perceptionof noise produced by the MRI system during operation.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A medical imaging scanner system comprising: a medical imagingscanner configured to scan an imaging subject within an imaging area,wherein the medical imaging scanner emits system noise when inoperation; and an emitter system constructed to emit an inaudible signalhaving properties to reduce auditory perception of the system noiseabout at least a portion of the imaging area.
 2. The medical imagingscanner system of claim 1 further comprising a parametric soundgenerator configured to generate a signal having properties to reduceperception of the system noise.
 3. The medical imaging scanner system ofclaim 1 wherein the medical imaging scanner is a magnetic resonanceimage scanner and the emitter system is arranged outside of a magneticfield of the magnetic resonance image scanner.
 4. The medical imagingscanner system of claim 1 wherein the emitter system includes anultrasonic emitter capable of columnular emissions.
 5. The medicalimaging scanner system of claim 4 wherein the ultrasonic emitter ismounted external to the medical imaging scanner.
 6. The medical imagingscanner system of claim 4 wherein the ultrasonic emitter is arrangedsuch that the columnular emissions are directed at a location to providean imaging subject with a substantially noise free environment.
 7. Themedical imaging scanner system of claim 1 wherein at least a portion ofthe emitter system is arranged a distance from the imaging area.
 8. Themedical imaging scanner system of claim 1 wherein the emitter system isdirected toward at least one of the imaging subject area and an operatorarea.
 9. The medical imaging scanner system of claim 1 furthercomprising another emitter system constructed to reduce perception ofsystem noise about at least a portion of an operator area.
 10. Themedical imaging scanner system of claim 1 wherein the emitter system isconfigured to directionally emit the inaudible signal.
 11. The medicalimaging scanner of claim 1 wherein the system noise reduction occursnear an imaging subject's ears.
 12. The medical imaging scanner systemof claim 1 wherein the emitter system includes an emitter that producesa column of ultrasonic energy in front of the emitter that containsproperties to produce cancellation audio frequencies when intermixedwith a non-linear medium.
 13. The medical imaging scanner system ofclaim 12 wherein the non-linear medium includes atmospheric air.
 14. Themedical imaging scanner system of claim 12 wherein the cancellationaudio frequencies are demodulated along the column of ultrasonic energy.15. The medical imaging scanner system of claim 14 wherein thedemodulated cancellation audio frequencies interact with the systemnoise to reduce perceivable system noise at the imaging area.
 16. Themedical imaging scanner system of claim 15 wherein the imaging area isan area of imaging subject sound reception.
 17. The medical imagingscanner system of claim 1 wherein the system noise is reduced asperceived by an imaging subject during a scanning operation.
 18. Amethod of medical imaging comprising: performing a medical imagingprocess upon an imaging subject, wherein the medical imaging processproduces a noise byproduct; and emitting an inaudible signal configuredto diminish auditory perception of the noise byproduct.
 19. The methodof claim 18 further comprising performing the medical imaging process onan imaging volume and emitting the inaudible signal outside of theimaging volume.
 20. The method of claim 18 further comprising columnlyemitting the inaudible signal to diminish auditory perception of thenoise byproduct within a selected volume.
 21. The method of claim 20wherein the selected volume includes one of an imaging volume and anoperating volume.
 22. The method of claim 18 further comprisingproducing a column of ultrasonic energy configured to interact withatmospheric air to produce anti-noise audio frequencies when intermixedwith an environmental air.
 23. The method of claim 18 wherein themedical imaging process includes a magnetic imaging resonance imagingprocess.
 24. An MRI apparatus comprising: an MRI system having aplurality of gradient coils positioned about a bore of a polarizingmagnet to impress a polarizing magnetic field, and an RF transceiversystem and an RF switch controlled by a pulse module to transmit RFsignals to an RF coil assembly to acquire MR images; and a parametricsignal generator configured to generate ultrasonic signals to reduceauditory perception of noise produced by the MRI system duringoperation.
 25. The MRI apparatus of claim 24 wherein the ultrasonicsignals are configured to induce anti-noise signals upon interactionwith environmental air.
 26. The MRI apparatus of claim 25 wherein theanti-noise signals are contained within a propagation column.
 27. TheMRI apparatus of claim 26 wherein the propagation column is focused onat least one of an operator area and the bore of the polarizing magnet.28. The MRI apparatus of claim 24 wherein the ultrasonic signals containmodulated ultrasonic audio frequencies configured to generatedemodulated cancellation audio frequencies upon interacting with anonlinear medium.
 29. The MRI apparatus of claim 28 wherein thedemodulated cancellation audio frequencies interact with noise producedby the MRI system to reduce perception of the noise.
 30. The MRIapparatus of claim 24 wherein the parametric signal generator isdisposed remotely from the MRI system.
 31. The MRI apparatus of claim 24further comprising an emitter configured to deliver an ultrasonic signalto at least a portion of the MRI system.